1. Field of the Invention
This invention relates to a device (hereinafter referred to as a "device of the kind specified"), particularly a tool of the pliers or scissors type, where it is desired that the force transmission ratio between the means which receive the driving power, such as a pair of manually operated handles in the case of pliers or scissors, and the means which perform the desired function such as cutting, pressing or the like, may be variable during the operation. As an example of a device of the kind specified so called crimping pliers may be named, which are a tool for crimping terminals provided with crimping barrels, so called ferrules, on the end of electrical wires or cables.
It is obvious that at the beginning of the crimping operation a smaller force is generally needed for the initial deformation of the crimping barrel than in the final stage, when the crimping barrel has to be tightly pressed towards the cable end to establish a reliable connection, electrical as well as mechanical. It is therefore preferable if the tool in the initial stages may be operated with a greater force transmission ratio than in the final phase, i.e., that at the end of the operation a smaller but stronger angular movement of the crimping jaws shall correspond to a given angular movement of the handles, executed with the same power, than at the beginning.
2. Description of the Prior Art
Various solutions of this problem have already been considered. It has been proposed in a vice-type tool with one rectilineary movable jaw (Swedish Pat. No. 205,961) to drive this jaw with the aid of a toggle joint mechanism where the free end of one link scans a cam surface on the inner edge of the movable handle. The solution is practicable only with vice-type tools and toggle joint mechanisms are in general rather complicated (expensive). A wire cutting tool has been proposed (U.S. Pat. No. 2,311,695) which is provided with such a lever arrangement that the force applied to the cutting elements or cutting jaws gradually increases as the cutting elements are moved together in accordance with the increase in resistance to cutting when the cut in the wire is increased. The arrangement is very bulky and demands a complicated lever system. Other known solutions of the problem are represented by tools, e.g., according to U.S. Pat. Nos. 1,820,169, 2,520,905, 3,273,240 or 3,390,455, where the increase in the cutting force or other active force occurs stepwise by a pawl jumping from one tooth to another in a rectilinear row of ratchet teeth. The pawl means and/or the teeth means require a separate lever organ, thus creating also a lever system, even if of somewhat simpler construction than according to the previously mentioned solution. The main drawback of the pawl-and-ratchet-solution is however the necessity to release the tension every time a force increasing jump of the pawl has to be executed, which makes this solution clearly unsuitable for many practical applications where continuous and/or continuously increasing action force is demanded.